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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Paolo Abeni <pabeni@redhat.com>,
        Eric Dumazet <edumazet@google.com>,
        "David S. Miller" <davem@davemloft.net>
Subject: [PATCH 5.13 143/156] tcp: consistently disable header prediction for mptcp
Date:   Thu, 22 Jul 2021 18:31:58 +0200
Message-Id: <20210722155632.970065618@linuxfoundation.org>
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From: Paolo Abeni <pabeni@redhat.com>

commit 71158bb1f2d2da61385c58fc1114e1a1c19984ba upstream.

The MPTCP receive path is hooked only into the TCP slow-path.
The DSS presence allows plain MPTCP traffic to hit that
consistently.

Since commit e1ff9e82e2ea ("net: mptcp: improve fallback to TCP"),
when an MPTCP socket falls back to TCP, it can hit the TCP receive
fast-path, and delay or stop triggering the event notification.

Address the issue explicitly disabling the header prediction
for MPTCP sockets.

Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/200
Fixes: e1ff9e82e2ea ("net: mptcp: improve fallback to TCP")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 include/net/tcp.h |    4 ++++
 1 file changed, 4 insertions(+)

--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -682,6 +682,10 @@ static inline u32 __tcp_set_rto(const st
 
 static inline void __tcp_fast_path_on(struct tcp_sock *tp, u32 snd_wnd)
 {
+	/* mptcp hooks are only on the slow path */
+	if (sk_is_mptcp((struct sock *)tp))
+		return;
+
 	tp->pred_flags = htonl((tp->tcp_header_len << 26) |
 			       ntohl(TCP_FLAG_ACK) |
 			       snd_wnd);